Recently, genome projects have progressed in respect of various organisms and a large number of genes including human genes, as well as their nucleotide sequences, are rapidly being clarified. The functions of the genes for which sequences have been clarified are being examined with various methods, and as one of these methods, gene expression analysis employing clarified sequence information is known. For example, various methods have been developed, such as Northern hybridization, which employ nucleic acid—nucleic acid hybridization reactions or which employ PCR reaction. These various methods have enabled examination of the relationship between various genes and the organic function expression thereof. However, there is a limit to the number of genes to which these methods can be applied. Therefore, given a complex reaction system constituted by a very large number of genes such as those clarified at an individual level by genome projects, there are difficulties in performing a generalized and systematic gene analysis with the above methods.
Recently, a new analysis method and methodology known as the DNA microarray method (DNA chip method) which allows one-operation expression analysis of numerous genes, has been developed and now attracts attention.
This method does not differ in principle from conventional methods in respect of the fact that it is nucleic acid detection and assay method based on nucleic acid-nucleic acid hybridization. However, a major characteristic of this method is the utilization of a large number of DNA fragments aligned and immobilized at high density on a flat substrate slice called a micro-array or chip. Examples of a specific method of using a micro-array method include for example hybridizing a sample of expression genes of a test subject cell labeled with fluorescent pigment on a flat substrate slice, allowing mutually complimentary nucleic acids (DNA or RNA) to bind with one another and after labeling these locations with fluorescent pigment, and rapidly reading with a high resolution analysis device. In this way, respective gene amounts in a sample can be rapidly estimated. That is, the essence of this new method is understood to be basically a combination of reduction of reaction sample amount and technology to arrange and align these reaction samples into a pattern allowing high volume, rapid, systematic analysis and quantification with good reproducibility.
Regarding techniques for immobilizing a nucleic acid on a substrate, apart from a method of high density immobilization on nylon sheets etc. such as in the above-mentioned Northern method, in order to further increase density, a method where polylysine is coated on a substrate of glass or the like, or a method involving direct solid phase synthesis of short-chain nucleic acids on a substrate of silicon or the like, are being developed.
However, while a spotting method of immobilization of nucleic acid on a substrate of glass or the like having an immobilization surface that is chemically or physically modified (Science 270, 467–470 (1995)) is superior to a sheet method in terms of spot density, it has been pointed out that in comparison to a direct synthesis method (U.S. Pat. No. 5,445,934, U.S. Pat. No. 5,774,305), spot density and amount of immobilized nucleic acid per spot are low and the method is inferior in terms of reproducibility. Alternatively, while a method involving solid phase synthesis of multiple short chain nucleic acids onto a silicon substrate in a regular manner using photolithography is superior in the number of types of nucleic acid able to be synthesized per unit of area (spot density), the amount immobilized per spot (synthesized amount), and reproducibility, the types of nucleic acid able to be immobilized are limited to relatively short-chained nucleic acids that are controllable with lithography. Further, it is difficult to effect a substantial reduction in cost per chip with this method due to the use of expensive manufacturing devices and multiple manufacturing steps. Also known as a method for solid phase synthesis of nucleic acid on a miniature carrier and library conversion thereof, is a method employing miniature beads. It is thought that this method enables synthesis of long chain nucleic acids with more types and at lower cost than a chip method, and also allows immobilization of longer nucleic acids such as cDNA, etc. However, differing from a chip method, it is difficult to produce a product such that specific compounds are arranged with good reproducibility according to a specific alignment standard.
Furthermore, when gene analysis is carried out using a currently available micro-array, it takes long time to perform hybridization and post-hybridization washing treatments.
An attempt to immobilize probe nucleic acid in a gel and detect hybridization with nucleic acid in a sample has been made (Japanese Patent Application Laying-Open (kokai) No. 3-47097, WO98/51823).
Examples of known methods involving the immobilization of nucleic acid in a gel include: a method involving the immobilization of aminated DNA in a copolymer gel having hydroxysuccinimide as a leaving group (Polym. Gel. Netw., 4, (2), 111 (1996)); a method involving the binding of aminated DNA to a polyacrylamide gel into which an aldehyde group is introduced (Nucleic Acid Res., 24, 3142 (1996)); a method involving the binding of aminated DNA to a polyacrylamide gel into which a mesyl group is introduced (ibid.); and a method involving the binding of aldehydated polyacrylamide to polyacrylamide into which a hydrazide group is introduced (Proc. Natl. Acad. Sci., 93, 4913 (1996)), etc.
Furthermore, methods involving filling a hollow fiber with gel is also being attempted. Examples of such methods include a method regarding the production of a capillary for electrophoresis described in Japanese Patent Application Laying-Open (kokai) No. 11-211694. In this method, a gel is formed in a hollow part during capillary spinning, thereby obtaining a capillary.
However, it is very likely that gel to be filled is easily removed from a hollow fiber due to polymerization shrinkage generally occurring during polymerization, and that the gel easily falls out of the hollow fiber. Accordingly, it was difficult to use a hollow fiber filled with gel for capillary electrophoresis or for a micro-array for DNA analysis. In general, gel existing in a micro-array is transparent, and so it was not easy to confirm the presence of gel at each site. Therefore, in respect of operability and practicality, a superior method was desired.